The position that wireless technologies will replace the PSTN meets with a number of objections. Primarily, these objections are focused on quality of service (QoS) issues, security of the wireless network, limitations in the range of the delivery of the service, and the availability of bandwidth. This book will explain how these objections have been overcome.
8.1.Quality of Service (QoS)
One of the primary concerns about guarantee of wireless data delivery, as with the Internet over wired services, is that the QoS is inadequate. Contention with other wireless
services, lost packets, and atmospheric interference are potential objections to WiMAX as an alternative to the PSTN. The need for QoS arises when there are multiple data streams competing for the limited physical capacity of the transmission media or network devices. In the case of WiMAX, the limiting resource is the radio frequency bandwidth. When there are multiple data streams competing to use the same frequency bandwidth, a QoS policy is needed to determine which data stream has the priority to use the air interface. This QoS policy depends on the user applications that are characterized by QoS
performance metrics. For example, an e-mail application does not need any guarantee except for reliable delivery of the data. A VoIP application needs guarantee of low latency. A video-streaming application can afford a long delay but requires relatively high bandwidth.
To support a wide variety of applications, WiMAX defines five scheduling services that should be supported by the base station MAC scheduler for data transport over a connection:
i. Unsolicited grant services (UGS): This is designed to support fixed-size data packets at a constant bit rate (CBR). Examples of applications that may use this service are T1/E1 emulation and VoIP without silence suppression. The mandatory service flow parameters that define this service are maximum sustained traffic rate, maximum latency, tolerated jitter and request/transmission policy.
ii. Real-time polling services (rtPS): This service is designed to support real-time service flows, such as MPEG video, that generate variable-size data packets on a periodic basis. The mandatory service flow parameters that define this service are minimum reserved traffic rate, maximum sustained traffic rate, maximum latency, and request/transmission policy.
iii. Non-real-time polling service (nrtPS): This service is designed to support delay-tolerant data streams, such as an FTP, that require variable-size data grants at a minimum guaranteed rate. The mandatory service flow parameters to define this service are minimum reserved traffic rate, maximum sustained traffic rate, traffic priority, and request/transmission policy.
iv. Best-effort (BE) service: This service is designed to support data streams, such as Web browsing, that do not require a minimum service-level guarantee. The mandatory service flow parameters to define this service are maximum sustained traffic rate, traffic priority and request/transmission policy.
v. Extended real-time variable rate (ERT-VR) service: This service is designed to support real-time applications, such as VoIP with silence suppression, that have variable data rates but require guaranteed data rate and delay. This service is defined only in IEEE 802.16e- 2005, not in IEEE 802.16-2004. This is also referred to as extended real-time polling service (ErtPS).
The WiMAX Forum Applications Working Group (AWG) has determined five initial application classes which is taken from www.WiMAXforum.org.
The QoS architecture framework developed by the WiMAX Forum extends the IEEE 802.16e QoS model by defining the various QoS-related functional entities in the WiMAX network and the mechanisms for provisioning and managing the various service flows and their associated policies. The WiMAX QoS framework supports simultaneous use of a diverse set of IP services, such as differentiated levels of QoS on a per user and per service flow basis, admission control, and bandwidth management. The QoS framework calls for the use of standard IETF mechanisms for managing policy decisions and policy enforcement between operators.
8.2. Power Saving
To support battery-operated portable devices, mobile WiMAX has power-saving features that allow portable subscriber stations to operate for longer durations without having to recharge. Power saving is achieved by turning off parts of the MS in a controlled manner when it is not actively transmitting or receiving data. Mobile WiMAX defines signaling methods that allow the MS to retreat into a sleep mode or idle mode when inactive.
- Sleep mode is a state in which the MS effectively turns itself off and becomes unavailable for predetermined periods. The periods of absence are negotiated with the serving BS. WiMAX defines three power-saving classes, based on the manner in which sleep mode is executed. When in Power Save Class 1 mode, the sleep window is exponentially increased from a minimum value to a maximum value. This is typically done when the MS is doing best-effort and non-real-time traffic. Power Save Class 2 has a fixed-length sleep window and is used for UGS service. Power Save Class 3 allows for a one-time sleep window and is typically used for multicast traffic or management traffic when the MS knows when the next traffic is expected. In addition to minimizing MS power consumption, sleep mode conserves BS radio resources. To facilitate handoff while in sleep mode, the MS is allowed to scan other base stations to collect handoff-related information.
- Idle mode allows even greater power savings, and support for it is optional in WiMAX. Idle mode allows the MS to completely turn off and to not be registered with any BS and yet receive downlink broadcast traffic. When downlink traffic arrives for the idle-mode MS, the MS is paged by a collection of base stations that form a paging group. The MS is assigned to a paging group by the BS before going into idle mode, and the MS periodically wakes up to update its paging group. Idle mode saves more power than sleep mode, since the MS does not even have to register or do handoffs. Idle mode also benefits the network and BS by eliminating handover traffic from inactive MSs.
8.3. Mobility Support
In addition to fixed broadband access, WiMAX envisions four mobility-related usage scenarios:
i. Nomadic: The user is allowed to take a fixed subscriber station and reconnect from a different point of attachment.
ii. Portable: Nomadic access is provided to a portable device, such as a PC card, with expectation of a best-effort handover.
iii. Simple mobility: The subscriber may move at speeds up to 60 km/h with brief interruptions (less than 1 sec) during handoff.
iv. Full mobility: Up to 120 km/h mobility and seamless handoff (less than 50 ms latency and <1% packet loss) is supported.
8.4. Security
Network security is a broad subject covering a number of areas. The most significant of those areas have to do with securing the network elements themselves. These encompass securing vital databases, including those concerned with customer records, network inventories, transactions with other service providers and carriers, and general business financial records; preventing unauthorized access onto the network and, in particular, preventing entry into customer virtual private networks (VPNs) or customer local area networks (LANs); preventing or limiting denial-of-service (DoS) attacks; and finally meeting CALEA reporting requirements imposed by the federal government in addition to other related regulatory mandates.
As well as securing network elements, software platforms, and customer and business databases, one has to consider securing a whole other area of security dealing with facilities management. Safeguarding the network from hacks performed over the Internet is certainly a worthy objective but is far from the only area upon which the network operator should focus:
i. Support for privacy: User data is encrypted using cryptographic schemes of proven robustness to provide privacy. Both AES (Advanced Encryption Standard) and 3DES (Triple Data Encryption Standard) are supported. Most system implementations will likely use AES, as it is the new encryption standard approved as compliant with Federal Information Processing Standard (FIPS) and is easier to implement.10 The 128-bit or 256-bit key used for deriving the cipher is generated during the authentication phase and is periodically refreshed for additional protection.
ii. Device/user authentication: WiMAX provides a flexible means for authenticating subscriber stations and users to prevent unauthorized use. The authentication framework is based on the Internet Engineering Task Force (IETF) EAP, which supports a variety of credentials, such as username/password, digital certificates, and smart cards. WiMAX terminal devices come with built-in X.509 digital certificates that contain their public key and MAC address. WiMAX operators can use the certificates for device authentication and use a username/password or smart card authentication on top of it for user authentication.
iii. Flexible key-management protocol: The Privacy and Key Management Protocol Version 2 (PKMv2) is used for securely transferring keying material from the base station to the mobile station, periodically reauthorizing and refreshing the keys. PKM is a client-server protocol: The MS acts as the client; the BS, the server. PKM uses X.509 digital certificates and RSA (Rivest- Shamer-Adleman) public-key encryption algorithms to securely perform key exchanges between the BS and the MS.
iv. Protection of control messages: The integrity of over-the-air control messages is protected by using message digest schemes, such as AES-based CMAC or MD5-based HMAC.11 Support for fast handover: To support fast handovers, WiMAX allows the MS to use preauthentication with a particular target BS to facilitate accelerated reentry. A three-way handshake scheme is supported to optimize the reauthentication mechanisms for supporting fast handovers, while simultaneously preventing any man-in-the-middle attacks.
8.5. Interference Mitigation
The Radio Act of 1927 has driven the wireless regulatory framework in the United States. It is time for change. The current Federal Communications Commission (FCC) is at least somewhat aware that wireless poses a third means (after the telephone company’s copper wire and the cable TV company’s coaxial cable) of delivering residential broadband and that when broadband Internet access is as ubiquitous as land line telephone service is today the U.S. economy can enjoy a $500 billion annual benefit.
The position that wireless technologies will replace the PSTN meets with a number of objections. Primarily, these objections are focused on quality of service (QoS) issues, security of the wireless network, limitations in the range of the delivery of the service, and the availability of bandwidth. This book will explain how these objections have been overcome.
8.1. Quality of Service (QoS)
One of the primary concerns about guarantee of wireless data delivery, as with the Internet over wired services, is that the QoS is inadequate. Contention with other wireless
services, lost packets, and atmospheric interference are potential objections to WiMAX as an alternative to the PSTN. The need for QoS arises when there are multiple data streams competing for the limited physical capacity of the transmission media or network devices. In the case of WiMAX, the limiting resource is the radio frequency bandwidth. When there are multiple data streams competing to use the same frequency bandwidth, a QoS policy is needed to determine which data stream has the priority to use the air interface. This QoS policy depends on the user applications that are characterized by QoS
performance metrics. For example, an e-mail application does not need any guarantee except for reliable delivery of the data. A VoIP application needs guarantee of low latency. A video-streaming application can afford a long delay but requires relatively high bandwidth.
To support a wide variety of applications, WiMAX defines five scheduling services that should be supported by the base station MAC scheduler for data transport over a connection:
i. Unsolicited grant services (UGS): This is designed to support fixed-size data packets at a constant bit rate (CBR). Examples of applications that may use this service are T1/E1 emulation and VoIP without silence suppression. The mandatory service flow parameters that define this service are maximum sustained traffic rate, maximum latency, tolerated jitter and request/transmission policy.
ii. Real-time polling services (rtPS): This service is designed to support real-time service flows, such as MPEG video, that generate variable-size data packets on a periodic basis. The mandatory service flow parameters that define this service are minimum reserved traffic rate, maximum sustained traffic rate, maximum latency, and request/transmission policy.
iii. Non-real-time polling service (nrtPS): This service is designed to support delay-tolerant data streams, such as an FTP, that require variable-size data grants at a minimum guaranteed rate. The mandatory service flow parameters to define this service are minimum reserved traffic rate, maximum sustained traffic rate, traffic priority, and request/transmission policy.
iv. Best-effort (BE) service: This service is designed to support data streams, such as Web browsing, that do not require a minimum service-level guarantee. The mandatory service flow parameters to define this service are maximum sustained traffic rate, traffic priority and request/transmission policy.
v. Extended real-time variable rate (ERT-VR) service: This service is designed to support real-time applications, such as VoIP with silence suppression, that have variable data rates but require guaranteed data rate and delay. This service is defined only in IEEE 802.16e- 2005, not in IEEE 802.16-2004. This is also referred to as extended real-time polling service (ErtPS).
The WiMAX Forum Applications Working Group (AWG) has determined five initial application classes which is taken from www.WiMAXforum.org.
The QoS architecture framework developed by the WiMAX Forum extends the IEEE 802.16e QoS model by defining the various QoS-related functional entities in the WiMAX network and the mechanisms for provisioning and managing the various service flows and their associated policies. The WiMAX QoS framework supports simultaneous use of a diverse set of IP services, such as differentiated levels of QoS on a per user and per service flow basis, admission control, and bandwidth management. The QoS framework calls for the use of standard IETF mechanisms for managing policy decisions and policy enforcement between operators.
8.2. Power Saving
To support battery-operated portable devices, mobile WiMAX has power-saving features that allow portable subscriber stations to operate for longer durations without having to recharge. Power saving is achieved by turning off parts of the MS in a controlled manner when it is not actively transmitting or receiving data. Mobile WiMAX defines signaling methods that allow the MS to retreat into a sleep mode or idle mode when inactive.
- Sleep mode is a state in which the MS effectively turns itself off and becomes unavailable for predetermined periods. The periods of absence are negotiated with the serving BS. WiMAX defines three power-saving classes, based on the manner in which sleep mode is executed. When in Power Save Class 1 mode, the sleep window is exponentially increased from a minimum value to a maximum value. This is typically done when the MS is doing best-effort and non-real-time traffic. Power Save Class 2 has a fixed-length sleep window and is used for UGS service. Power Save Class 3 allows for a one-time sleep window and is typically used for multicast traffic or management traffic when the MS knows when the next traffic is expected. In addition to minimizing MS power consumption, sleep mode conserves BS radio resources. To facilitate handoff while in sleep mode, the MS is allowed to scan other base stations to collect handoff-related information.
- Idle mode allows even greater power savings, and support for it is optional in WiMAX. Idle mode allows the MS to completely turn off and to not be registered with any BS and yet receive downlink broadcast traffic. When downlink traffic arrives for the idle-mode MS, the MS is paged by a collection of base stations that form a paging group. The MS is assigned to a paging group by the BS before going into idle mode, and the MS periodically wakes up to update its paging group. Idle mode saves more power than sleep mode, since the MS does not even have to register or do handoffs. Idle mode also benefits the network and BS by eliminating handover traffic from inactive MSs.
8.3. Mobility Support
In addition to fixed broadband access, WiMAX envisions four mobility-related usage scenarios:
i. Nomadic: The user is allowed to take a fixed subscriber station and reconnect from a different point of attachment.
ii. Portable: Nomadic access is provided to a portable device, such as a PC card, with expectation of a best-effort handover.
iii. Simple mobility: The subscriber may move at speeds up to 60 km/h with brief interruptions (less than 1 sec) during handoff.
iv. Full mobility: Up to 120 km/h mobility and seamless handoff (less than 50 ms latency and <1% packet loss) is supported.
8.4. Security
Network security is a broad subject covering a number of areas. The most significant of those areas have to do with securing the network elements themselves. These encompass securing vital databases, including those concerned with customer records, network inventories, transactions with other service providers and carriers, and general business financial records; preventing unauthorized access onto the network and, in particular, preventing entry into customer virtual private networks (VPNs) or customer local area networks (LANs); preventing or limiting denial-of-service (DoS) attacks; and finally meeting CALEA reporting requirements imposed by the federal government in addition to other related regulatory mandates.
As well as securing network elements, software platforms, and customer and business databases, one has to consider securing a whole other area of security dealing with facilities management. Safeguarding the network from hacks performed over the Internet is certainly a worthy objective but is far from the only area upon which the network operator should focus:
i. Support for privacy: User data is encrypted using cryptographic schemes of proven robustness to provide privacy. Both AES (Advanced Encryption Standard) and 3DES (Triple Data Encryption Standard) are supported. Most system implementations will likely use AES, as it is the new encryption standard approved as compliant with Federal Information Processing Standard (FIPS) and is easier to implement.10 The 128-bit or 256-bit key used for deriving the cipher is generated during the authentication phase and is periodically refreshed for additional protection.
ii. Device/user authentication: WiMAX provides a flexible means for authenticating subscriber stations and users to prevent unauthorized use. The authentication framework is based on the Internet Engineering Task Force (IETF) EAP, which supports a variety of credentials, such as username/password, digital certificates, and smart cards. WiMAX terminal devices come with built-in X.509 digital certificates that contain their public key and MAC address. WiMAX operators can use the certificates for device authentication and use a username/password or smart card authentication on top of it for user authentication.
iii. Flexible key-management protocol: The Privacy and Key Management Protocol Version 2 (PKMv2) is used for securely transferring keying material from the base station to the mobile station, periodically reauthorizing and refreshing the keys. PKM is a client-server protocol: The MS acts as the client; the BS, the server. PKM uses X.509 digital certificates and RSA (Rivest- Shamer-Adleman) public-key encryption algorithms to securely perform key exchanges between the BS and the MS.
iv. Protection of control messages: The integrity of over-the-air control messages is protected by using message digest schemes, such as AES-based CMAC or MD5-based HMAC.11
Support for fast handover: To support fast handovers, WiMAX allows the MS to use preauthentication with a particular target BS to facilitate accelerated reentry. A three-way handshake scheme is supported to optimize the reauthentication mechanisms for supporting fast handovers, while simultaneously preventing any man-in-the-middle attacks.
8.5. Interference Mitigation
The Radio Act of 1927 has driven the wireless regulatory framework in the United States. It is time for change. The current Federal Communications Commission (FCC) is at least somewhat aware that wireless poses a third means (after the telephone company’s copper wire and the cable TV company’s coaxial cable) of delivering residential broadband and that when broadband Internet access is as ubiquitous as land line telephone service is today the U.S. economy can enjoy a $500 billion annual benefit.
WiMAX Uses
The Technology Of WiMAX